Here’s a photo essay on building a 15mm machine gun nest.
Modeling
Making 15mm Vegetable Crop Fields
Big Lee’s Miniature Adventures has an illustrated tutorial on making model 15mm vegetable fields from corded dormats.
Making A Command and Colors Terrain Table
Small World Productions has a tutorial on making a “hex” based terrain table for Command and Colors.
Cheap 28mm Paved Roads
The Frozen Gamer has an article on making asphalt roads from vinyl strips.
Building A “Classic” Wargames Windmill
The Lead Gardens blog has an illustrated article on building a “classic” wargames windmill.